Polymers containing hydroxamate groups have been known to be particularly useful for the flocculation of red muds produced in the Bayer process, see U.S. Pat. No. 4,767,540. These polymers are generally produced by reacting aqueous solutions of the polymers, e.g. polyacrylamide, with hydroxylamine salts. When the molecular weight of the polymer being hydroxamated is of such a value that the polymer performs at its best in the flocculation application, it has hitherto been in the form of a highly viscous gel. The high viscosity of the gel causes major handling problems both during and after hydroxamation since high viscosity fluids are extremely difficult to transfer from one vessel to another e.g. from reactor to storage, from storage to shipment container and from shipment container to application. The viscosity of such a gel is particularly high when the molecular weight of the polymer is high, i.e. over about 1,000,000.
Furthermore, it is customary for polymers of such high viscosities to be pre-diluted, usually in water, before they are used, so that they may be more easily mixed into the substrate which is to be subjected to flocculation. The high viscosity of hydroxamated polymer gels makes this a difficult process to undertake and often requires the use of specialized and expensive equipment. These inherent limitations in such gels necessarily means that the solids content of such gel products must be kept as low as possible in order to maintain the viscosity at a practical level, i.e. the lower the solids content, the lower the viscosity. The shipment costs of low solids solutions of polymer, however, are significantly higher because of the dilution.
In the case of conventional acrylamide polymers, the viscosity problems have been largely overcome through the development of high solids water-in-oil microdispersions, i.e. such forms as microemulsions, emulsions, microsuspensions, and as used herein, such term is meant to include said forms. As small micelles, the high viscosity polymers, while still being, in effect, gels themselves, are nevertheless, more easily dissolved in the substrates to which they are added in use. Thus, where a polymer solution at high solids is a stiff gel, a microdispersion of the same gel is more easily handled and used due to its lower viscosity.
Attempts have been made to create stable microdispersions of hydroxamated polymers in the past, see U.S. Pat. Nos. 4,587,306; 4,767,540 and 4,868,248. Due to the complexities of performing the hydroxamation reaction in this product form, however, it has not been previously possible to satisfactorily accomplish this goal. The problems attendant such hydroxamation reactions include poor incorporation of the hydroxamate functionality, poor stability of the emulsion, i.e. phase separation after relatively short periods of standing, insolubilization of the polymer, molecular weight degradation etr.
U.S. Pat. No. 4,587,306 to Vio discloses a method for preparing hydroxamated polymer emulsions from polyacrylamide backbones of low molecular weight, e.g. 4000 or below. There is no evidence, however, that the material produced was a true polymer dispersion in oil or, in fact, even an oil-in-water type. It is known that the problem of reacting a polymer backbone with a reagent becomes more acute when the molecular weight of the polymer is high. Attempts to produce, by the method taught in U.S. Pat. No. 4,587,306, both low and high molecular weight, stable, gel-free, water-in-oil hydroxamated polymer emulsions have shown that the incorporation of hydroxamate functionality is much lower (and insignificant) than shown therein for the claimed low molecular weight polymers. Furthermore, at the elevated reaction temperatures thereof, e.g. 70.degree. C., it is very difficult to form a stable emulsion if, in fact one can be formed at all. Indeed, the examples below show that a stable, gel-free high molecular eight, hydroxamated polymer emulsion was not formed under the reaction conditions of this patent at room temperature or at 70.degree. C. Thus, it is clear that the process of the '306 patent is not suitable for the preparation of the microdispersions claimed herein. A further distinction worth noting is that the mole ratio of KOH to hydroxylamine hydrochloride used by the process of U.S. Pat. No. 4,587,306 is only 0.78, i.e. the hydroxylamine is only partially neutralized and the reaction is therefore conducted under acidic conditions which limits the rate of the reaction and necessitates the use of extreme temperatures which further causes the formation of unstable products.
In U.S. Pat. No. 4,767,540 there is disclosed a method for the production of hydroxamated polyacrylamides in which there is proported to be produced a stable emulsion of hydroxamated polyacrylamide. However, attempts to duplicate the procedure of this patent have proven to be less than successful in that the resultant products are not stable, gel-free, water-in-oil microdispersions, see Examples 34 and 35, below.
U.S. Pat. No. 4,868,248 discloses that emulsions of hydroxamated polymers can be produced; however, the patentee fails to disclose any specific example to the production of such a polymer. Both methods described for preparing the polymers thereof are solution-based and no water-in-oil microdispersions are shown.
Accordingly, the search continues for a method for the production of stable, gel-free microdispersions of hydroxamated vinyl polymers, i.e. one in which the structural integrity of the microdispersion remains in tact and is pourable.